AKT ligands and polynucleotides encoding AKT ligands

ABSTRACT

The invention relates to kinase ligands and polyligands. In particular, the invention relates to ligands, homopolyligands, and heteropolyligands that modulate AKT activity. The ligands, homopolyligands, and heteropolyligands are utilized as research tools or as therapeutics. The invention includes linkage of the ligands, homopolyligands, and heteropolyligands to a cellular localization signal, epitope tag and/or a reporter. The invention also includes polynucleotides encoding the ligands, homopolyligands, and heteropolyligands.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 60/803,913, filed Jun. 5, 2006, the entirety of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to mammalian kinase ligands, substrates and modulators. In particular, the invention relates to polypeptides, polypeptide compositions and polynucleotides that encode polypeptides that are ligands, substrates, and/or modulators of AKT. The invention also relates to polyligands that are homopolyligands or heteropolyligands that modulate AKT activity.

This application has subject matter related to application Ser. Nos. 10/724,532 (US 2004/0203027), 10/682,764 (US2004/0185556, PCT/US2004/013517, WO2005/040336), 11/233,246, and US20040572011P (WO2005116231). Each of these applications is hereby incorporated by reference.

2. Background of the Invention

Kinases are enzymes that catalyze the addition of phosphate to a molecule. The addition of phosphate by a kinase is called phosphorylation. When the kinase substrate is a protein molecule, the amino acids commonly phosphorylated are serine, threonine and tyrosine. Phosphatases are enzymes that remove phosphate from a molecule. The removal of phosphate is called dephosphorylation. Kinases and phosphatases often represent competing forces within a cell to transmit, attenuate, or otherwise modulate cellular signals and cellular control mechanisms. Kinases and phosphatases have both overlapping and unique natural substrates. Cellular signals and control mechanisms, as regulated by kinases, phosphatases, and their natural substrates are a target of research tool design and drug design.

Mammalian Protein Kinase B is also known as AKT. The enzymatic activity, activation and autoregulation of AKT have been studied. Several cellular substrates of AKT have been identified. A pharmacological agent that inhibits AKT activity has been disclosed in the literature by Martelli et al. (Leukemia (2003) 17:1794-1805). Natural and synthetic polypeptides have been studied to examine AKT substrate specificity. While polypeptides and variants thereof have been studied as individual AKT substrates or ligands, mixed ligands linked together as polyligands that modulate AKT activity have not been demonstrated before this invention. An aspect of the invention is to provide novel, modular, inhibitors of AKT activity by modifying one or more natural substrates either by truncation or by amino acid substitution. A further aspect of the invention is the subcellular localization of an AKT inhibitor, ligand, or polyligand by linking to a subcellular localization signal.

Design and synthesis of polypeptide ligands that modulate calcium/calmodulin-dependent protein kinase and that localize to the cardiac sarco(endo)plasmic reticulum was performed by Ji et al. (J Biol Chem (2003) 278:25063-71). Ji et al. accomplished this by generating expression constructs that localized calcium/calmodulin-dependent protein kinase inhibitory polypeptide ligands to the sarcoplasmic reticulum by fusing a sarcoplasmic reticulum localization signal derived from phospholamban to a polypeptide ligand. See also US 2004/0203027.

The following references are hereby incorporated in their entirety: Altiok et al. 1999 J Biol Chem 274:32274-32278; Alessi et al. 1996 J FEBS Letters 399:333-338; Berwick et al. 2002 J Biol Chem 277:33895-33900; Biggs III et al. 1999 Genetics 96:7421-7426; Blume-Jensen et al. 1998 Current Biol 8:779-782; Brazil et al. 2002 Cell 111:293-303; Brunet et al. 1999 Cell 96:857-868; Cardone et al. 1998 Science 282:1318-1321; Cha et al. 2005 Science 310: 306-310; Chen et al. 2003 Cell 133:457-468; Cross et al. 1995 Nature 378:785-789; Datta et al. 1999 J Genes and Dev. 13:2905-2927; Deprez et al. 1997 J Biol Chem; Du et al. 2003 Science 300:1574-1577; Gingras et al. 1998 Genes and Dev. 12:502-513; Hanada et al. 2004 Biochimica 1697:3-16; Humbert et al. 2002 Dev Cell 2(6):831-837; Hurt et al. 2002 J PNAS 99:4061-4066; Lee et al. 2001 mol. Cell 8(3):693-704; Li et al. 1999 J Biol Chem 274:9351-9356; Jiang et al. 2005 J Biol Chem 280:21622-21628; Kane et al. 2002 J Biol Chem 277:22115-22118; Kitamura et al. 1999 Mol cell Biol 19:6286-6296; Kovacina et al. 2003 J Biol Chem 278:10189-10194; Kwon et al. 2000 J Biol Chem 275:423-428; Lawlor et al. 2001 J Cell Science 114:2903-2910; Lynch et al. 2002 EMBO 21:72-82; Maira et al. 2001 Science 294:374-380; Michell et al. 1999 Current Biol 9:845-848; Miinea et al. 2005 Biochem 391:87-93; Nakae et al. 2001 J. Clin. Invest. 108:1359-1367; Obata et al. 2000 J Biol Chem 275:36108-36115; Ozes et al. 1999 Nature 401:82-85; Peso et al. 1997 Science 278:687-689; Plomgaard et al. 2005 Diabetes 54:2939-2945; Powell et al. 2002 J Biol Chem 277:21639-21642; Rena et al. 1999 J Biol Chem 274:17179-17183; Saito et al. 2004 J Neuroscience 24:1584-1593; Sano et al. 2003 J Biol Chem 278:14599-14602; Song et al. 2005 J Cell. Mol. Med. 9:59-71; Tee et al. 2003 J Biol Chem 278:37288-37296; Toker et al. 2000 J Biol Chem 275:8271-8274; Viglietto et al. 2002 Nature Medicine 8:1136-1144; Vitari et al. 2004 J Biochem 378:257-268; Wang et al. 2005 Mol Pharmacol 67:489-498; Wolfrum et al. 2003 PNAS 100:11624-11629; Yang et al. 2005 J Biol Chem 280:33558-33565; Yang et al. 2002 J Nature Structural Biol 9:940-944; Zheng et al. 2000 J Biol Chem 275:39152-39158; Zhou et al. 2002 Semin. Oncology 3(11):62-70; Zhou et al. 2003 Mol Cell Biol 23(22):8058-8069; Zimmerman et al. 1999 Science 286:1741-1744.

SUMMARY OF THE INVENTION

The invention relates to mammalian kinase ligands, substrates and modulators. In particular, the invention relates to polypeptides, polypeptide compositions and polynucleotides that encode polypeptides that are ligands, substrates, and/or modulators of AKT. The invention also relates to polyligands that are homopolyligands or heteropolyligands that modulate AKT activity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C show examples of homopolymeric ligands without spacers.

FIGS. 2A-2C show examples of homopolymeric ligands with spacers.

FIGS. 3A-3E show examples of heteropolymeric ligands without spacers.

FIGS. 4A-4E show examples of heteropolymeric ligands with spacers.

FIGS. 5A-5G show examples of ligands and polymeric ligands linked to an epitope tag.

FIGS. 6A-6G show examples of ligands and polymeric ligands linked to a reporter.

FIGS. 7A-7G show examples of ligands and polymeric ligands linked to a localization signal.

FIGS. 8A-8G show examples of ligands and polymeric ligands linked to a localization signal and an epitope tag.

FIGS. 9A-9G show examples of gene constructs where ligands and polyligands are linked to a localization signal, an epitope tag, and a reporter.

FIGS. 10A-10D show examples of vectors containing ligand gene constructs.

FIG. 11 shows an example of a sequential cloning process useful for combinatorial synthesis of polyligands.

FIG. 12 shows a diagram of the vector used to transform the Huh7 cells of FIG. 13.

FIG. 13 shows an example of the effects of a nuclear-localized AKT polyligand on FKHRL1-GFP cellular distribution. Inhibition of AKT kinase using the AKT polyligand changed the translocation of the Forkhead transcription factor (FKHRL1), causing nuclear retention in Huh7 cells. Panels A-C represent Huh7 cells transfected with a FKHRL1-Green Fluorescent Protein (GFP) fusion protein, under normal growth conditions, 24 hours posttransfection. Panels D-G represent Huh7 cells co-transfected with the AKT polyligand and FKHRL1-GFP fusion protein 24 hours posttransfection. Panel D represents anti c-Myc primary and secondary antibody staining specific to the c-Myc epitope tag linked to the AKT polyligand. Panels A and E represent GFP fluorescent imaging to recognize the FKHRL1-GFP fusion protein. Panel B and F represent DAPI nuclear DNA staining, (4′,6-diamidino-2-phenylindole) staining, a standard fluorescent stain for visualizing nuclear DNA, to determine the number and position of Huh7 cell nuclei. Panel C and G represent a co-localization of all panels in that represented row. Panel C shows that under normal growth conditions, the concentration of FKHRL1-GFP is primarily outside the nucleus. Panel G shows the FKHRL1-GFP fusion protein inside the nucleus, in those cells where the AKT polyligand is also present.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to ligands and polyligands that are AKT modulators. The ligands and polyligands comprise SEQ ID NOS:1-261. Polyligands are chimeric ligands comprising two or more monomeric polypeptide ligands. An example of a monomeric ligand is the polypeptide represented by SEQ ID NO:83, wherein Xaa is any amino acid. SEQ ID NO:83 is a selected subsequence of wildtype full length SEQ ID NO:10, wherein the amino acid corresponding to Xaa in the wildtype sequence is a serine or threonine phosphorylatable by AKT. Another example of a monomeric ligand is the polypeptide represented by SEQ ID NO:74. Each of SEQ ID NOS:74-261 represents an individual polypeptide ligand in monomeric form, wherein Xaa is any amino acid. SEQ ID NOS:83-261 are selected examples of subsequences of SEQ ID NOS:10-73, however, other subsequences of SEQ ID NOS:10-73 may also be utilized as monomeric ligands. Monomeric ligand subsequences of SEQ ID NOS:10-73 may be wildtype subsequences. Additionally, monomeric ligand subsequences of SEQ ID NOS:10-73 may have the AKT phosphorylatable amino acids replaced by other amino acids. Furthermore, monomeric ligands and polyligands may have at least about 80%, 85%, 90%, 95%, 96%, 97%, 98% or 99% sequence identity to a ligand comprising an amino acid sequence in one or more of SEQ ID NOS:74-261. Furthermore, monomeric ligands and polyligands may have at least about 80%, 85%, 90%, 95%, 96%, 97%, 98% and 99% sequence identity to a subsequence of SEQ ID NOS:10-73.

SEQ ID NOS:1-9 are example polyligands and polynucleotides encoding them. Specifically, the AKT polyligand of SEQ ID NO:1 is encoded by SEQ ID NO:2 and by SEQ ID NO:3, wherein the codons of SEQ ID NO:3 have been optimized for vector insertion. A vector map of a vector containing SEQ ID NO:3 is shown in FIG. 12 (labeled AKT decoy). SEQ ID NO:1 was expressed in Huh7 cells as shown in FIG. 13. SEQ ID NO:1 is an embodiment of a polyligand of the structure A-B-C-D, wherein A is SEQ ID NO:74, B is SEQ ID NO:75, C is SEQ ID NO:76, and D is SEQ ID NO:77. A polyligand of structure A-B-C-D is also called herein a heteropolyligand.

SEQ ID NO:4 is an embodiment of a polyligand of the structure X-Y-Z, wherein X is SEQ ID NO:84, Y is SEQ ID NO:119, and Z is SEQ ID NO:86, and wherein Xaa is Alanine. The AKT polyligand of SEQ ID NO:4 is encoded by SEQ ID NO:5 and by SEQ ID NO:6, wherein the codons of SEQ ID NO:6 have been optimized for vector insertion. A polyligand of structure X-Y-Z is also called herein a heteropolyligand.

SEQ ID NO:7 is an embodiment of a polyligand of the structure X-S1-Y-S2-Z, wherein X is SEQ ID NO:131, Y is SEQ ID NO:88, Z is SEQ ID NO: 137, wherein Xaa is Alanine, and wherein S1 is a five amino acid spacer with the sequence AlaGlyAlaGlyPro, and S2 is a five amino acid spacer with the sequence GlyAlaGlyAlaPro. The AKT polyligand of SEQ ID NO:7 is encoded by SEQ ID NO:8 and by SEQ ID NO:9, wherein the codons of SEQ ID NO:9 have been optimized for vector insertion. A polyligand of structure X-S1-Y-S2-Z is also called herein a heteropolyligand.

SEQ ID NOS:10-73 are full length AKT protein substrates. These sequences have the following public database accession numbers: AAA51780, NP 055655, NP_(—)055647, Q8BYJ6, Q99683, NP_(—)000323, NP_(—)058683, NP_(—)001087, NP_(—)031548, AAC37594, AAD24962, BAA82697, AAC51817, NP_(—)604391, CAA53712, P21453, O08530, NP_(—)000594, AAS09975, NP_(—)002006, NP_(—)963853, CAA63819, NP_(—)710141, NP_(—)062713, NP_(—)062714, BAA76737, BAA76738, NP_(—)000804, NP_(—)001026837, AAA62432, AAH00251, NP_(—)062801, AAH61044, AAI06721, NP_(—)002102, O15111, NP_(—)005535, AAB09030, NP_(—)002383, NP_(—)002410, P42345, P30414, NP_(—)775180, AAB29246, NP_(—)004055, AAB95193, Q15121, NP_(—)000297, CAA06606, NP_(—)035185, NP_(—)000913, AAH07416, NP_(—)002818, CAB53579, AAH92040, NP_(—)003001, NP_(—)003210, NP_(—)005195, P49815, Q61037, Q9H4A3, P46937, NP_(—)663723, P31749. Each of the sequences represented by these accession numbers is incorporated by reference herein.

SEQ ID NOS:74-82 represent examples of monomeric peptide ligand sequences, wherein Xaa is any amino acid.

SEQ ID NOS:83-261 are partial sequences of SEQ ID NOS:10-73, which represent examples of peptide ligand sequences where the location of the AKT phosphorylatable serine or threonine in the natural polypeptide is designated as Xaa.

SEQ ID NOS:79-261 encompass peptides where Xaa is any amino acid. In some embodiments, Xaa is serine or threonine.

An example of a homopolyligand is a polypeptide comprising a dimer or multimer of SEQ ID NO:83, wherein Xaa is any amino acid. An example of a heteropolyligand is a polypeptide comprising SEQ ID NO:74 and one or more of SEQ ID NOS:75-261, wherein Xaa is any amino acid. There are numerous ways to combine SEQ ID NOS:74-261 into homopolymeric or heteropolymeric ligands. Furthermore, there are numerous ways to combine additional subsequences of SEQ ID NOS:10-73 with each other and with SEQ ID NOS:74-261 to make polymeric ligands.

Polyligands may comprise any two or more of SEQ ID NOS:74-261, wherein Xaa is any amino acid. A dimer or multimer of SEQ ID NO:118 is an example of a homopolyligand. An example of a heteropolyligand is a polypeptide comprising SEQ ID NO:261 and one or more of SEQ ID NOS:74-260. There are numerous ways to combine SEQ ID NOS:74-261 into homopolymeric or heteropolymeric ligands. SEQ ID NOS:83-261 are selected examples of subsequences of SEQ ID NOS:10-73, however, additional subsequences, wildtype or mutated, may be utilized to form polyligands. The instant invention is directed to all possible combinations of homopolyligands and heteropolyligands without limitation.

SEQ ID NOS:10-73 show proteins that contain at least one serine or threonine residue phosphorylatable by AKT. SEQ ID NOS:83-261 are subsequences of SEQ ID NOS:10-73 where the locations of the AKT phosphorylatable residues are represented by Xaa. In nature, Xaa is, generally speaking, serine or threonine. In one embodiment of the instant invention, Xaa can be any amino acid. Ligands where Xaa is serine or threonine can be used as part of a polyligand, however in one embodiment, the phosphorylatable serine or threonine is replaced with another amino acid, such as one of the naturally occurring amino acids including, alanine, aspartate, asparagine, cysteine, glutamate, glutamine, phenylalanine, glycine, histidine, isoleucine, leucine, lysine, methionine, proline, arginine, valine, tryptophan, or tyrosine. The Xaa may also be a non-naturally occurring amino acid. In another embodiment, the AKT phosphorylatable serine(s) or threonine(s) are replaced by alanine. As shown by SEQ ID NO: 1 and FIG. 13 and Example 4 below, the polyligands of the invention are capable of modulating endogenous effects of AKT.

In general, ligand monomers are built by isolating a putative AKT phosphorylation recognition motif in an AKT substrate. Sometimes it is desirable to modify the phosphorylatable residue to an amino acid other than serine or threonine. Additional monomers include the AKT recognition motif as well as amino acids adjacent and contiguous on either side of the AKT recognition motif Monomers may therefore be any length provided the monomer includes the AKT recognition motif For example, the monomer may comprise an AKT recognition motif and at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30-100 or more amino acids adjacent to the recognition motif.

For example, in one embodiment, the invention comprises an inhibitor of AKT comprising at least one copy of a peptide selected from the group consisting of: a) a peptide at least 80%, 85%, 90%, 95%, 96%, 97%, 98% or 99% identical to a peptide comprising amino acid residues corresponding to amino acid residues 203-209 of the amino acid sequence of SEQ ID NO:10, wherein the amino acid residue corresponding to amino acid residue 208 of SEQ ID NO:10 has been mutated to an amino acid residue other than serine or threonine; b) a peptide at least 80%, 85%, 90%, 95%, 96%, 97%, 98% or 99% identical to a peptide comprising amino acid residues corresponding to amino acid residues 200-212 of the amino acid sequence of SEQ ID NO:10, wherein the amino acid residue corresponding to amino acid residue 208 of SEQ ID NO:10 has been mutated to an amino acid residue other than serine or threonine; c) a peptide at least 80%, 85%, 90%, 95%, 96%, 97%, 98% or 99% identical to a peptide comprising amino acid residues corresponding to amino acid residues 193-219 of the amino acid sequence of SEQ ID NO:10, wherein the amino acid residue corresponding to amino acid residue 208 of SEQ ID NO:10 has been mutated to an amino acid residue other than serine or threonine; and d) a peptide at least 80%, 85%, 90%, 95%, 96%, 97%, 98% or 99% identical to a peptide comprising amino acid residues corresponding to amino acid residues 183-229 of the amino acid sequence of SEQ ID NO:10, wherein the amino acid residue corresponding to amino acid residue 208 of SEQ ID NO:10 has been mutated to an amino acid residue other than serine or threonine.

As used herein, the terms “correspond(s) to” and “corresponding to,” as they relate to sequence alignment, are intended to mean enumerated positions within a reference protein, e.g., Androgen Receptor (SEQ ID NO:10), and those positions that align with the positions on the reference protein. Thus, when the amino acid sequence of a subject peptide is aligned with the amino acid sequence of a reference peptide, e.g., SEQ ID NO:10, the amino acids in the subject peptide sequence that “correspond to” certain enumerated positions of the reference peptide sequence are those that align with these positions of the reference peptide sequence, but are not necessarily in these exact numerical positions of the reference sequence. Methods for aligning sequences for determining corresponding amino acids between sequences are described below.

Additional embodiments of the invention include monomers (as described above) based on any putative or real substrate for AKT, such as substrates identified by SEQ ID NOS:11-73. Furthermore, if the substrate has more than one recognition motif, then more than one monomer may be identified therein.

Another embodiment of the invention is a nucleic acid molecule comprising a polynucleotide sequence encoding at least one copy of a ligand peptide.

Another embodiment of the invention is a nucleic acid molecule wherein the polynucleotide sequence encodes one or more copies of one or more peptide ligands.

Another embodiment of the invention is a nucleic acid molecule wherein the polynucleotide sequence encodes at least a number of copies of the peptide selected from the group consisting of 2, 3, 4, 5, 6, 7, 8, 9 or 10.

Another embodiment of the invention is a vector comprising a nucleic acid molecule encoding at least one copy of a ligand peptide.

Another embodiment of the invention is a recombinant host cell comprising a vector comprising a nucleic acid molecule encoding at least one copy of a ligand peptide.

Another embodiment of the invention is a method of inhibiting AKT in a cell comprising transfecting a vector comprising a nucleic acid molecule encoding at least one copy of a ligand peptide into a host cell and culturing the transfected host cell under conditions suitable to produce at least one copy of the peptide.

The invention also relates to modified inhibitors that are at least about 80%, 85%, 90% 95%, 96%, 97%, 98% or 99% identical to a reference inhibitor. A “modified inhibitor” is used to mean a peptide that can be created by addition, deletion or substitution of one or more amino acids in the primary structure (amino acid sequence) of a inhibitor protein or polypeptide. A “modified recognition motif” is a naturally occurring AKT recognition motif that has been modified by addition, deletion, or substitution of one or more amino acids in the primary structure (amino acid sequence) of the motif. For example, a modified AKT recognition motif may be a motif where the phosphorylatable amino acid as been modified to a non-phosphorylatable amino acid. The terms “protein” and “polypeptide” are used interchangeably herein. The reference inhibitor is not necessarily a wild-type protein or a portion thereof. Thus, the reference inhibitor may be a protein or peptide whose sequence was previously modified over a wild-type protein. The reference inhibitor may or may not be the wild-type protein from a particular organism. Furthermore, the term “wild-type protein” includes the wild-type protein with or without a leader sequence.

A polypeptide having an amino acid sequence at least, for example, about 95% “identical” to a reference an amino acid sequence is understood to mean that the amino acid sequence of the polypeptide is identical to the reference sequence except that the amino acid sequence may include up to about five modifications per each 100 amino acids of the reference amino acid sequence encoding the reference peptide. In other words, to obtain a peptide having an amino acid sequence at least about 95% identical to a reference amino acid sequence, up to about 5% of the amino acid residues of the reference sequence may be deleted or substituted with another amino acid or a number of amino acids up to about 5% of the total amino acids in the reference sequence may be inserted into the reference sequence. These modifications of the reference sequence may occur at the N-terminus or C-terminus positions of the reference amino acid sequence or anywhere between those terminal positions, interspersed either individually among amino acids in the reference sequence or in one or more contiguous groups within the reference sequence.

As used herein, “identity” is a measure of the identity of nucleotide sequences or amino acid sequences compared to a reference nucleotide or amino acid sequence. In general, the sequences are aligned so that the highest order match is obtained. “Identity” per se has an art-recognized meaning and can be calculated using published techniques. (See, e.g., Computational Molecular Biology, Lesk, A. M., ed., Oxford University Press, New York (1988); Biocomputing: Informatics And Genome Projects, Smith, D. W., ed., Academic Press, New York (1993); Computer Analysis of Sequence Data, Part I, Griffin, A. M., and Griffin, H. G., eds., Humana Press, New Jersey (1994); von Heinje, G., Sequence Analysis In Molecular Biology, Academic Press (1987); and Sequence Analysis Primer, Gribskov, M. and Devereux, J., eds., M Stockton Press, New York (1991)). While there exist several methods to measure identity between two polynucleotide or polypeptide sequences, the term “identity” is well known to skilled artisans (Carillo, H. & Lipton, D., Siam J Applied Math 48:1073 (1988)). Methods commonly employed to determine identity or similarity between two sequences include, but are not limited to, those disclosed in Guide to Huge Computers, Martin J. Bishop, ed., Academic Press, San Diego (1994) and Carillo, H. & Lipton, D., Siam J Applied Math 48:1073 (1988). Computer programs may also contain methods and algorithms that calculate identity and similarity. Examples of computer program methods to determine identity and similarity between two sequences include, but are not limited to, GCG program package (Devereux, J., et al., Nucleic Acids Research 12(i):387 (1984)), BLASTP, ExPASy, BLASTN, FASTA (Atschul, S. F., et al., J Molec Biol 215:403 (1990)) and FASTDB. Examples of methods to determine identity and similarity are discussed in Michaels, G. and Garian, R., Current Protocols in Protein Science, Vol 1, John Wiley & Sons, Inc. (2000), which is incorporated by reference. In one embodiment of the present invention, the algorithm used to determine identity between two or more polypeptides is BLASTP.

In another embodiment of the present invention, the algorithm used to determine identity between two or more polypeptides is FASTDB, which is based upon the algorithm of Brutlag et al. (Comp. App. Biosci. 6:237-245 (1990), incorporated by reference). In a FASTDB sequence alignment, the query and subject sequences are amino sequences. The result of sequence alignment is in percent identity. Parameters that may be used in a FASTDB alignment of amino acid sequences to calculate percent identity include, but are not limited to: Matrix=PAM, k-tuple=2, Mismatch Penalty=1, Joining Penalty=20, Randomization Group Length=0, Cutoff Score=1, Gap Penalty=5, Gap Size Penalty 0.05, Window Size=500 or the length of the subject amino sequence, whichever is shorter

If the subject sequence is shorter or longer than the query sequence because of N-terminus or C-terminus additions or deletions, not because of internal additions or deletions, a manual correction can be made, because the FASTDB program does not account for N-terminus and C-terminus truncations or additions of the subject sequence when calculating percent identity. For subject sequences truncated at the 5′ or 3′ ends, relative to the query sequence, the percent identity is corrected by calculating the number of bases of the query sequence that are N- and C-terminus to the reference sequence that are not matched/aligned, as a percent of the total bases of the query sequence. The results of the FASTDB sequence alignment determine matching/alignment. The alignment percentage is then subtracted from the percent identity, calculated by the above FASTDB program using the specified parameters, to arrive at a final percent identity score. This corrected score can be used for the purposes of determining how alignments “correspond” to each other, as well as percentage identity. Residues of the query (subject) sequences or the reference sequence that extend past the N- or C-termini of the reference or subject sequence, respectively, may be considered for the purposes of manually adjusting the percent identity score. That is, residues that are not matched/aligned with the N- or C-termini of the comparison sequence may be counted when manually adjusting the percent identity score or alignment numbering.

For example, a 90 amino acid residue subject sequence is aligned with a 100 residue reference sequence to determine percent identity. The deletion occurs at the N-terminus of the subject sequence and therefore, the FASTDB alignment does not show a match/alignment of the first 10 residues at the N-terminus. The 10 unpaired residues represent 10% of the sequence (number of residues at the N- and C-termini not matched/total number of residues in the query sequence) so 10% is subtracted from the percent identity score calculated by the FASTDB program. If the remaining 90 residues were perfectly matched the final percent identity would be 90%. In another example, a 90 residue subject sequence is compared with a 100 reference sequence. This time the deletions are internal deletions so there are no residues at the N- or C-termini of the subject sequence which are not matched/aligned with the query. In this case the percent identity calculated by FASTDB is not manually corrected.

The polyligands of the invention optionally comprise spacer amino acids between monomers. The length and composition of the spacer may vary. An example of a spacer is glycine, alanine, polyglycine, or polyalanine. Specific examples of spacers used between monomers in SEQ ID NO:7 are the five amino acid peptides GlyAlaGlyAlaPro and AlaGlyAlaGlyPro. In the instance of SEQ ID NO:7, the proline-containing spacer is intended to break an alpha helical secondary structure. Spacer amino acids may be any amino acid and are not limited to alanine, glycine and proline. SEQ ID NO:7, depicted generically in FIG. 4B, represents a specific example of a heteropolyligand with the structure X-S1-Y-S2-Z, where X is SEQ ID NO:131, Y is SEQ ID NO:88, Z is SEQ ID NO: 137, wherein Xaa is Alanine, and wherein S1 is a five amino acid spacer with the sequence AlaGlyAlaGlyPro, and S2 is a five amino acid spacer with the sequence GlyAlaGlyAlaPro. The instant invention is directed to all combinations of homopolyligands and heteropolyligands, with or without spacers, and without limitation to the examples given above or below.

The ligands and polyligands of the invention are optionally linked to additional molecules or amino acids that provide an epitope tag, a reporter, and/or localize the ligand to a region of a cell. Non-limiting examples of epitope tags are FLAG™ (Kodak; Rochester, N.Y.), HA (hemaglutinin), c-Myc and His6. Additional examples of epitope tags are given in Jarvik & Telmer 1998 Annual Reviw of Genetics 32:601-18. Non-limiting examples of reporters are alkaline phosphatase, galactosidase, peroxidase, luciferase and green fluorescent protein (GFP). Non-limiting examples of cellular localizations are sarcoplamic reticulum, endoplasmic reticulum, mitochondria, golgi apparatus, nucleus, plasma membrane, apical membrane, and basolateral membrane. The epitopes, reporters and localization signals are given by way of example and without limitation. The epitope tag, reporter and/or localization signal may be the same molecule. The epitope tag, reporter and/or localization signal may also be different molecules.

Ligands and polyligands and optional amino acids linked thereto can be synthesized chemically or recombinantly using techniques known in the art. Chemical synthesis techniques include but are not limited to peptide synthesis which is often performed using an automated peptide synthesizer. Peptides can also be synthesized utilizing non-automated peptide synthesis methods known in the art. Recombinant techniques include insertion of ligand-encoding nucleic acids into expression vectors, wherein nucleic acid expression products are synthesized using cellular factors and processes.

Linkage of a cellular localization signal, epitope tag, or reporter to a ligand or polyligand can include covalent or enzymatic linkage to the ligand. When the localization signal comprises material other than a polypeptide, such as a lipid or carbohydrate, a chemical reaction to link molecules may be utilized. Additionally, non-standard amino acids and amino acids modified with lipids, carbohydrates, phosphate or other molecules may be used as precursors to peptide synthesis. The ligands of the invention have therapeutic utility with or without localization signals. For example, the ligands generically depicted in FIGS. 1A-1C, FIGS. 2A-2C, FIGS. 3A-3C, FIGS. 4A-4C and FIGS. 7A-7G represent embodiments of conventional polypeptide therapeutics. However, ligands linked to localization signals have utility as subcellular tools or therapeutics. For example, ligands depicted generically in FIGS. 7A-7G represent ligands with utility as subcellular tools or therapeutics. AKT ligand-containing gene constructs are also delivered via gene therapy. FIGS. 10B and 10C depict embodiments of gene therapy vectors for delivering and controlling polypeptide expression in vivo. Polynucleotide sequences linked to the gene construct in FIGS. 10B and 10C include genome integration domains to facilitate integration of the transgene into a viral genome and/or host genome.

FIG. 10A shows a vector containing an AKT ligand gene construct, wherein the ligand gene construct is releasable from the vector as a unit useful for generating transgenic animals. For example, the ligand gene construct, or transgene, is released from the vector backbone by restriction endonuclease digestion. The released transgene is then injected into pronuclei of fertilized mouse eggs; or the transgene is used to transform embryonic stem cells. The vector containing a ligand gene construct of FIG. 10A is also useful for transient transfection of the trangene, wherein the promoter and codons of the transgene are optimized for the host organism. The vector containing a ligand gene construct of FIG. 10A is also useful for recombinant expression of polypeptides in fermentible organisms adaptable for small or large scale production, wherein the promoter and codons of the transgene are optimized for the fermentation host organism.

FIG. 10D shows a vector containing an AKT ligand gene construct useful for generating stable cell lines.

The invention also encompasses polynucleotides comprising nucleotide sequences encoding ligands, homopolyligands, and heteropolyligands. The polynucleotides of the invention are optionally linked to additional nucleotide sequences encoding epitopes, reporters and/or localization signals. Further, the nucleic acids of the invention are optionally incorporated into vector polynucleotides. The polynucleotides are optionally flanked by nucleotide sequences comprising restriction endonuclease sites and other nucleotides needed for restriction endonuclease activity. The flanking sequences optionally provide cloning sites within a vector. The restriction sites can include, but are not limited to, any of the commonly used sites in most commercially available cloning vectors. Examples of such sites are those recognized by BamHI, ClaI, EcoRI, EcoRV, SpeI, AflII, NdeI, NheI, XbaI, XhoI, SphI, NaeI, SexAI, HindIII, HpaI, and PstI restriction endonucleases. Sites for cleavage by other restriction enzymes, including homing endonucleases, are also used for this purpose. The polynucleotide flanking sequences also optionally provide directionality of subsequence cloning. It is preferred that 5′ and 3′ restriction endonuclease sites differ from each other so that double-stranded DNA can be directionally cloned into corresponding complementary sites of a cloning vector.

Ligands and polyligands with or without localization signals, epitopes or reporters are alternatively synthesized by recombinant techniques. Polynucleotide expression constructs are made containing desired components and inserted into an expression vector. The expression vector is then transfected into cells and the polypeptide products are expressed and isolated. Ligands made according to recombinant DNA techniques have utility as research tools and/or therapeutics.

The following is an example of how polynucleotides encoding ligands and polyligands are produced. Complimentary oligonucleotides encoding the ligands and flanking sequences are synthesized and annealed. The resulting double-stranded DNA molecule is inserted into a cloning vector using techniques known in the art. When the ligands and polyligands are placed in-frame adjacent to sequences within a transgenic gene construct that is translated into a protein product, they form part of a fusion protein when expressed in cells or transgenic animals.

Another embodiment of the invention relates to selective control of transgene expression in a desired cell or organism. The promotor portion of the recombinant gene can be a constitutive promotor, a non-constitutive promotor, a tissue-specific promotor (constitutive or non-constitutive) or a selectively controlled promotor. Different selectively controlled promoters are controlled by different mechanisms. For example, a tetracycline-inducible promotor is activated to express a downstream coding sequence when the cell containing the promotor and other necessary cellular factors is treated with tetracycline. When tetracycline is removed, gene expression is subsequently reduced. Other inducible promotors are activated by other drugs or factors. RheoSwitch® is an inducible promotor system available from RheoGene. Temperature sensitive promoters can also be used to increase or decrease gene expression. An embodiment of the invention comprises a ligand or polyligand gene construct whose expression is controlled by an inducible promotor. In one embodiment, the inducible promotor is tetracycline inducible.

Polyligands are modular in nature. An aspect of the instant invention is the combinatorial modularity of the disclosed polyligands. Another aspect of the invention are methods of making these modular polyligands easily and conveniently. In this regard, an embodiment of the invention comprises methods of modular subsequence cloning of genetic expression components. When the ligands, homopolyligands, heteropolyligands and optional amino acid expression components are synthesized recombinantly, one can consider each clonable element as a module. For speed and convenience of cloning, it is desirable to make modular elements that are compatible at cohesive ends and are easy to insert and clone sequentially. This is accomplished by exploiting the natural properties of restriction endonuclease site recognition and cleavage. One aspect of the invention encompasses module flanking sequences that, at one end of the module, are utilized for restriction enzyme digestion once, and at the other end, utilized for restriction enzyme digestion as many times as desired. In other words, a restriction site at one end of the module is utilized and destroyed in order to effect sequential cloning of modular elements. An example of restriction sites flanking a coding region module are sequences recognized by the restriction enzymes NgoM IV and Cla I; or Xma I and Cla I. Cutting a first circular DNA with NgoM IV and Cla I to yield linear DNA with a 5′ NgoM IV overhang and a 3′ Cla I overhang; and cutting a second circular DNA with Xma I and Cla I to yield linear DNA with a 5′ Cla I overhang and a 3′ Xma I overhang generates first and second DNA fragments with compatible cohesive ends. When these first and second DNA fragments are mixed together, annealed, and ligated to form a third circular DNA fragment, the NgoM IV site that was in the first DNA and the Xma I site that was in the second DNA are destroyed in the third circular DNA. Now this vestigial region of DNA is protected from further Xma I or NgoM IV digestion, but flanking sequences remaining in the third circular DNA still contain intact 5′ NgoM IV and 3′ Cla I sites. This process can be repeated numerous times to achieve directional, sequential, modular cloning events. Restriction sites recognized by NgoM IV, Xma I, and Cla I endonucleases represent a group of sites that permit sequential cloning when used as flanking sequences. This process is depicted in FIG. 11.

Another way to assemble coding region modules directionally and sequentially employs linear DNA in addition to circular DNA. For example, like the sequential cloning process described above, restriction sites flanking a coding region module are sequences recognized by the restriction enzymes NgoM IV and Cla I; or Xma I and Cla I. A first circular DNA is cut with NgoM IV and Cla I to yield linear DNA with a 5′ NgoM IV overhang and a 3′ Cla I overhang. A second linear double-stranded DNA is generated by PCR amplification or by synthesizing and annealing complimentary oligonucleotides. The second linear DNA has 5′ Cla I overhang and a 3′ Xma I overhang, which are compatible cohesive ends with the first DNA linearized. When these first and second DNA fragments are mixed together, annealed, and ligated to form a third circular DNA fragment, the NgoM IV site that was in the first DNA and the Xma I site that was in the second DNA are destroyed in the third circular DNA. Flanking sequences remaining in the third circular DNA still contain intact 5′ NgoM IV and 3′ Cla I sites. This process can be repeated numerous times to achieve directional, sequential, modular cloning events. Restriction sites recognized by NgoM IV, Xma I, and Cla I endonucleases represent a group of sites that permit sequential cloning when used as flanking sequences.

One of ordinary skill in the art recognizes that other restriction site groups can accomplish sequential, directional cloning as described herein. Preferred criteria for restriction endonuclease selection are selecting a pair of endonucleases that generate compatible cohesive ends but whose sites are destroyed upon ligation with each other. Another criteria is to select a third endonuclease site that does not generate sticky ends compatible with either of the first two. When such criteria are utilized as a system for sequential, directional cloning, ligands, polyligands and other coding regions or expression components can be combinatorially assembled as desired. The same sequential process can be utilized for epitope, reporter, and/or localization signals.

Polyligands and methods of making polyligands that modulate AKT activity are disclosed. Therapeutics include delivery of purified ligand or polyligand with or without a localization signal to a cell. Alternatively, ligands and polyligands with or without a localization signals are delivered via adenovirus, lentivirus, adeno-associated virus, or other viral constructs that express protein product in a cell.

Ligands of the invention can be assayed for kinase modulating activity several methods.

In one embodiment, a biochemical assay can be performed employing commercially-obtained kinase, commercially-obtained substrate, commercially-obtained kinase inhibitor (control), and semi-purified inhibitor ligand of the invention (decoy ligand). Decoy ligands can be linked to an epitope tag at one end of the polypeptide for purification and/or immobilization, for example, on a microtiter plate. The tagged decoy ligand can be made using an in vitro transcription/translation system such as a reticulocyte lysate system well known in the art. A vector polynucleotide comprising a promotor, such as T7 and/or T3 and/or SP6 promotor, a decoy ligand coding sequence, and an epitope tag coding sequence can be employed to synthesize the tagged decoy ligand in an in vitro transcription/translation system. In vitro transcription/translation protocols are disclosed in reference manuals such as: Current Protocols in Molecular Biology (eds. Ausubel et al., Wiley, 2004 edition.) and Molecular Cloning: A Laboratory Manual (Sambrook and Russell (Cold Spring Harbor Laboratory Press, 2001, third edition). Immunoreagent-containing methods such as western blots, elisas, and immunoprecipitations can be performed as described in: Using Antibodies: A Laboratory Manual (Harlow and Lane Cold Spring Harbor Laboratory Press, 1999).

In another embodiment, specifically, tagged decoy ligand synthesized using an in vitro transcription/translation system can be semi-purified and added to a microtiter plate containing kinase enzyme and substrate immobilized by an anti-substrate specific antibody. Microtiter plates can be rinsed to substantially remove non-immobilized components. Kinase activity is a direct measure of the phosphorylation of substrate by kinase employing a phospho-substrate specific secondary antibody conjugated to horseradish peroxidase (HRP) followed by the addition of 3,3′,5,5′-tetramethylbenzidine (TMB) substrate solution. The catalysis of TMB by HRP results in a blue color that changes to yellow upon addition of phosphoric or sulfuric acid with a maximum absorbance at 450 nm. Control experiments can include the absence of kinase enzyme, and/or absence of decoy ligand, and/or presence/absence of known kinase inhibitors. A known kinase inhibitor useful in the assay is staurosporine.

A similar assay can be performed employing the same reagents as above but the substrate can be biotinylated and immobilized by binding to a streptavidin-coated plate.

In another embodiment, a biochemical assay can be performed employing commercially-obtained kinase, commercially-obtained substrate, commercially-obtained kinase inhibitor (control), and semi-purified inhibitor ligand of the invention (decoy ligand) in a microtiter plate. A luminescent-based detection system, such as Promega's Kinase-Glo, can then be added to inversely measure kinase activity.

In yet another embodiment, specifically, tagged decoy ligand synthesized using an in vitro transcription/translation system can be semi-purified and added to a microtiter plate containing kinase enzyme and substrate. After the kinase assay is performed, luciferase and luciferin are added to the reaction. Luciferase utilizes any remaining ATP not used by the kinase to catalyze luciferin. The luciferase reaction results in the production of light which is inversely related to kinase activity. Control experiments can include the absence of kinase enzyme, and/or absence of decoy ligand, and/or presence/absence of known kinase inhibitors. A known kinase inhibitor useful in the assay is staurosporine.

In another embodiment still, a similar cell-based assay can be performed employing the same reagents as above, but synthesizing the decoy ligand in a mammalian cell system instead of an in vitro transcription/translation system. Decoy ligands can be linked to an epitope tag at one end of the polypeptide for immobilization and/or for purification and/or for identification in a western blot. Optionally, tagged decoy ligands can also be linked to a cellular localization signal for phenotypic comparison of pan-cellular and localized kinase modulation. A vector polynucleotide comprising a constitutive promotor, such as the CMV promotor, a decoy ligand coding sequence, an epitope tag coding sequence, and optionally a localization signal coding sequence can be employed to express the decoy ligand in cells. Transfection and expression protocols are disclosed in reference manuals such as: Current Protocols in Molecular Biology (eds. Ausubel et al., Wiley, 2004 edition.) and Molecular Cloning: A Laboratory Manual (Sambrook and Russell (Cold Spring Harbor Laboratory Press, 2001, third edition). Western Blots and immunoreagent-containing methods can be performed as described in: Using Antibodies: A Laboratory Manual (Harlow and Lane Cold Spring Harbor Laboratory Press, 1999).

EXAMPLES Example 1

A polypeptide comprising a heteropolyligand, an endoplasmic reticulum cellular localization signal, and a His6 epitope is synthesized. The structure of such a polypeptide is generically represented by FIG. 8E. The polypeptide is synthesized on an automated peptide synthesizer or is recombinantly expressed and purified. Purified polypeptide is solubilized in media and added to cells. The polypeptide is endocytosed by the cells, and transported to the endoplasmic reticulum. Verification is performed by immunohistochemical staining using an anti-His6 antibody.

Example 2

A transgene is constructed using a human cytomegalovirus (CMV) promoter to direct expression of a fusion protein comprising SEQ ID NO:84, SEQ ID NO:119, SEQ ID NO:86 (POLYLIGAND), green fluorescent protein (REPORTER), and a plasma membrane localization signal (LOCALIZATION SIGNAL). Such a transgene is generically represented by FIG. 9C. The transgene is transfected into cells for transient expression. Verification of expression and location is performed by visualization of green fluorescent protein (GFP) by confocal microscopy.

Example 3

A transgene construct is built to produce a protein product with expression driven by a tissue-specific promoter. The transgene comprises a synthetic gene expression unit engineered to encode three domains. Each of these three domains is synthesized as a pair of complimentary polynucleotides that are annealed in solution, ligated and inserted into a vector. Starting at the amino-terminus, the three domains in the expression unit are nucleotide sequences that encode an AKT ligand, a FLAG™ epitope, and a nuclear localization signal. The AKT ligand is a monomeric ligand, homopolymeric ligand or heteropolymeric ligand as described herein. Nucleotide sequences encoding a FLAG™ epitope (amino acids DYKDDDDK) are placed downstream of nucleotide sequences encoding the AKT ligand. Finally, nucleotide sequences encoding the localization signal are placed downstream of those encoding the FLAG™ epitope. The assembled gene expression unit is subsequently subcloned into an expression vector, such as that shown in FIG. 10A, and used to transiently transfect cells. Verification is performed by immunohistochemical staining using an anti-FLAG™ antibody.

Example 4

Modulation of AKT cellular function by subcellularly localized AKT polyligand was demonstrated in Huh7 cells. A transgene construct containing a polyligand fusion protein, epitope, and nuclear localization signal was made. The expressed portion of the transgene construct is generically shown in FIG. 8A. The expression unit contains nucleotides that encode SEQ ID NO:1 (POLYLIGAND), a c-Myc epitope (EPITOPE), and a nuclear localization signal (LOCALIZATION SIGNAL). This expression unit is subsequently subcloned into a vector between a CMV promoter and an SV40 polyadenylation signal (Generically depicted in FIG. 10A). The completed transgene-containing expression vector is then used to transfect Huh7 cells co-transfected with FKHRL1-GFP fusion expression construct. FIG. 13 illustrates the change in cellular location of FKHRL1-GFP when co-expressed with nuclear-localized AKT ligand. In the absence of nuclear-localized AKT ligand, FKHRL1-GFP is primarily outside the nucleus. However, in the presence of nuclear-localized AKT ligand, FKHRL1-GFP is primarily inside the nucleus.

Example 5

Ligand function and localization is demonstrated in vivo by making a transgene construct used to generate mice expressing a ligand fusion protein targeted to the endoplasmic reticulum. The transgene construct is shown generically in FIG. 10B. The expression unit contains nucleotides that encode a tetramer of SEQ ID NO:74, a hemaglutinin epitope, and a mitochondrial localization signal. This expression unit is subsequently subcloned into a vector between nucleotide sequences including an inducible promoter and an SV40 polyadenylation signal. The completed transgene is then injected into pronuclei of fertilized mouse oocytes. The resultant pups are screened for the presence of the transgene by PCR. Transgenic founder mice are bred with wild-type mice. Heterozygous transgenic animals from at least the third generation are used for the following tests, with their non-transgenic littermates serving as controls.

Test 1: Southern blotting analysis is performed to determine the copy number. Southern blots are hybridized with a radio-labeled probe generated from a fragment of the transgene. The probe detects bands containing DNA from transgenic mice, but does not detect bands containing DNA from non-transgenic mice. Intensities of the transgenic mice bands are measured and compared with the transgene plasmid control bands to estimate copy number. This demonstrates that mice in Example 4 harbor the transgene in their genomes.

Test 2: Tissue homogenates are prepared for Western blot analysis. This experiment demonstrates the transgene is expressed in tissues of transgenic mice because hemaglutinin epitope is detected in transgenic homogenates but not in non-transgenic homogenates.

These examples demonstrate delivery of ligands to a localized region of a cell for therapeutic or experimental purposes. The purified polypeptide ligands can be formulated for oral or parenteral administration, topical administration, or in tablet, capsule, or liquid form, intranasal or inhaled aerosol, subcutaneous, intramuscular, intraperitoneal, or other injection; intravenous instillation; or any other routes of administration. Furthermore, the nucleotide sequences encoding the ligands permit incorporation into a vector designed to deliver and express a gene product in a cell. Such vectors include plasmids, cosmids, artificial chromosomes, and modified viruses. Delivery to eukaryotic cells can be accomplished in vivo or ex vivo. Ex vivo delivery methods include isolation of the intended recipient's cells or donor cells and delivery of the vector to those cells, followed by treatment of the recipient with the cells.

Disclosed are ligands and polyligands that modulate AKT activity and methods of making and using these ligands. The ligands and polyligands are synthesized chemically or recombinantly and are utilized as research tools or as therapeutics. The invention includes linking the ligands and polyligands to cellular localization signals for subcellular therapeutics. 

1. A polypeptide comprising the structure A-B-C-D, wherein each of A, B, C and D is a different polypeptide monomer, wherein A is a polypeptide monomer comprising an amino acid sequence at least 85% identical to SEQ ID NO: 74, B is a polypeptide monomer comprising an amino acid sequence at least 85% identical to SEQ ID NO: 75, C is a polypeptide monomer comprising an amino acid sequence at least 85% identical to SEQ ID NO: 76, D is a polypeptide monomer comprising an amino acid sequence at least 85% identical to SEQ ID NO: 77, and wherein said polypeptide modulates AKT activity.
 2. The polypeptide of claim 1, wherein A is a polypeptide monomer comprising an amino acid sequence at least about 90% identical to SEQ ID NO: 74, B is a polypeptide monomer comprising an amino acid sequence at least about 90% identical to SEQ ID NO: 75, C is a polypeptide monomer comprising an amino acid sequence at least about 90% identical to SEQ ID NO: 76, and D is a polypeptide monomer comprising an amino acid sequence at least about 90% identical to SEQ ID NO:
 77. 3. The polypeptide of claim 2, wherein A is a polypeptide monomer comprising an amino acid sequence at least about 95% identical to SEQ ID NO: 74, B is a polypeptide monomer comprising an amino acid sequence at least about 95% identical to SEQ ID NO: 75, C is a polypeptide monomer comprising an amino acid sequence at least about 95% identical to SEQ ID NO: 76, and D is a polypeptide monomer comprising an amino acid sequence at least about 95% identical to SEQ ID NO:
 77. 4. The polypeptide of claim 3, wherein A is a polypeptide monomer comprising an amino acid sequence at least about 96% identical to SEQ ID NO: 74, B is a polypeptide monomer comprising an amino acid sequence at least about 96% identical to SEQ ID NO: 75, C is a polypeptide monomer comprising an amino acid sequence at least about 96% identical to SEQ ID NO: 76, and D is a polypeptide monomer comprising an amino acid sequence at least about 96% identical to SEQ ID NO:
 77. 5. The polypeptide of claim 4, wherein A is a polypeptide monomer comprising an amino acid sequence at least about 97% identical to SEQ ID NO: 74, B is a polypeptide monomer comprising an amino acid sequence at least about 97% identical to SEQ ID NO: 75, C is a polypeptide monomer comprising an amino acid sequence at least about 97% identical to SEQ ID NO: 76, and D is a polypeptide monomer comprising an amino acid sequence at least about 97% identical to SEQ ID NO:
 77. 6. The polypeptide of claim 5, wherein A is a polypeptide monomer comprising an amino acid sequence at least about 98% identical to SEQ ID NO: 74, B is a polypeptide monomer comprising an amino acid sequence at least about 98% identical to SEQ ID NO: 75, C is a polypeptide monomer comprising an amino acid sequence at least about 98% identical to SEQ ID NO: 76, and D is a polypeptide monomer comprising an amino acid sequence at least about 98% identical to SEQ ID NO:
 77. 7. The polypeptide of claim 6, wherein A is a polypeptide monomer comprising an amino acid sequence at least about 99% identical to SEQ ID NO: 74, B is a polypeptide monomer comprising an amino acid sequence at least about 99% identical to SEQ ID NO: 75, C is a polypeptide monomer comprising an amino acid sequence at least about 99% identical to SEQ ID NO: 76, and D is a polypeptide monomer comprising an amino acid sequence at least about 99% identical to SEQ ID NO:
 77. 8. The polypeptide of claim 1, further comprising at least one spacer.
 9. The polypeptide of claim 1, wherein said polypeptide comprises the amino acid sequence of SEQ ID NO:
 1. 10. The polypeptide of claim 1, further comprising a cellular localization signal.
 11. The polypeptide of claim 10, further comprising an amino acid sequence encoding an epitope.
 12. The polypeptide of claim 10, further comprising an amino acid sequence encoding a reporter. 